1. Field of the Invention
The present invention relates to flame retardant polyphenylene ether compositions and, more specifically, to blends of a polyphenylene ether resin and a high impact polystyrene in which a polybrominated 1,4-diphenoxybenzene and antimony oxide are used in combination to provide better flame resistance with less juicing and good thermal stability.
2. Description of the Prior Art
Thermoplastic compositions of polyphenylene ether (oxide) resins and high impact polystyrenes are known to be useful for injection molding into a variety of articles characterized by highly desirable property profiles. With the wider use of these compositions in products where good flame resistance is an important requirement, the need has grown for additives that upgrade the flame retardance of the composition without detracting from other desired properties.
Common flame retardant additives for polyphenylene ether blends include halogenated, and especially brominated, compounds. Often these are used in combination with other flame retardant agents, such as aromatic phosphates, and with synergistic flame retardancy enhancers such as antimony oxide. The patent literature describes a number of polyphenylene ether compositions modified with such types of agents, for example, U.S. Pat. No. 3,639,506 (Haaf), U.S. Pat. No. 3,671,487 (Abolins), and U.S. Pat. No. 4,355,126 (Haaf and Reinhard). The conventional halogenated flame retardant compounds in particular include halogenated diphenyl ethers, for example, decabromodiphenyl oxide, as disclosed in the just mentioned U.S. Pat. No. 4,355,126.
Shortcomings usually associated with the use of brominated compounds include poor thermal stability (the compounds break down at the elevated temperatures normal for processing, and the byproducts contaminate the polymer and can hasten its degradation); and an unfortunate tendency to juice or bloom, that is, to migrate to the surface of the composition in the mold and to volatilize (this eventually leads to corrosion of the mold interiors due to the presence of bromine in the volatilized materials).